In September, Twitter rolled out a redesign to its users profile pages that featured header photos.
"On December 12, we're rolling this out to all users: you'll automatically get this new version of the profile on twitter.com. If you don't upload a header photo by then, you (and everyone else) will only see a default grey image on your page. That's not fun!" the company said.
If you're not sure how to upload a header photo on your Twitter page, the social network has a how-to video that breaks the process down.